Stereoscopic imaging apparatus

ABSTRACT

A stereoscopic imaging apparatus includes: an objective optical system having a function of imaging a subject as a real image or a virtual image; and plural imaging optical systems that image plural subject luminous fluxes output from different paths of the objective optical system again as parallax images using plural independent optical systems, wherein, in the case where a focal length value when the objective optical system images the subject as the real image is positive and the focal length value when the objective optical system images the subject as the virtual image is negative, a focal distance (f) of the objective optical system and a distance (L) from a rear principal point of the objective optical system to a front principal point of the imaging optical system is set to values that satisfy the following equation
 
| f /( L−f )|≤1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/287,712, filed Nov. 2, 2011, which is hereby incorporated byreference in its entirety. Foreign priority benefits are claimed under35 U.S.C. 119(a)-(d) or 35 U.S. C. 365 (b) of Japanese Application No.2010-251750, filed Nov. 10, 2010.

FIELD

The present disclosure relates to a stereoscopic imaging apparatus thatshoots stereoscopic images, and specifically, to a technology ofadjusting a base line length as a distance between lenses of plurallenses for imaging stereoscopic images.

BACKGROUND

Recently, demand for cameras (stereoscopic imaging apparatuses) that mayshoot 3D (stereoscopic) images has been getting stronger. As an imagingmethod of stereoscopic images, a beam splitter method (half mirrormethod) of shooting using a half mirror, a side-by-side method(side-by-side twin-eye method) of shooting using two imaging apparatusesplaced physically side by side, etc. are known. In these shootingmethods, the imaging apparatuses are mounted on a pedestal called Rigfor shooting, and the degree of freedom in mounting of the imagingapparatus is higher. For example, the distance between lenses of twolenses for shooting of stereoscopic images (base line length;hereinafter, referred to as IAD: InterAxial Distance), convergence,angle of view, etc. may be selected with the high degree of freedom.

However, while the degree of freedom is high, there is a problem thatlots of efforts and time are necessary for setting and adjustment withrespect to each shooting because the apparatuses are mounted on the rig.Further, there is a problem that the rig for the beam splitter method issignificantly large-scaled and not suitable for use of shooting in thefields and interviews.

To solve the problems, two 2D video shooting cameras for shooting by theside-by-side method are incorporated in one housing to form anintegrated two-eye 3D camera. The integrated two-eye 3D camera havingthe configuration does not need assembly or adjustment of alignment.Further, the camera is compact and easy to carry at shooting in thefields and interviews and has an advantage to promptly start shootingafter setup in a short time.

However, the integrated two-eye 3D camera is basically according to theside-by-side method, and adjustment of IAD is limited. That is, therespective optical systems and imagers of the two eyes physicallyinterfere with each other, and IAD is difficult to be made shorter thana certain distance determined depending on the placement positions ofthe optical systems and imagers. Accordingly, for example, in the casewhere shooting is performed very close to a subject, parallax when thesubject is displayed on a 3D display several meters behind it exceedsthe range of parallax when a human can comfortably view 3D images.

As the cases where the subject and the imaging apparatus is very close,for example, shooting of an interview of a person, shooting at thebackyard in sports broadcasting, etc. are conceivable. In the cases, thedistance between the subject and the imaging apparatus is about 1 to 2 mand the convergence point is set to the distance of 1 to 2 m. In thecases, the most useful IAD for bringing the parallax within the range inwhich a human can comfortably view 3D images is considered to be 10 mmto 40 mm. However, in the current two-eye 3D camera, it is difficult torealize the short IAD while keeping image quality and functions, i.e.,without reducing the diameters of lenses or sizes of the imagers.

In the case where shooting is performed according to the above describedbeam splitter method, two imaging apparatuses do not physicallyinterfere with each other and the IAD can be made very short. However,as described above, there is the problem that lots of efforts and timeare necessary for setting and adjustment with respect to each shooting,and the problem that the method is not suitable for shooting of aninterview of a person or shooting at the backyard in sports broadcastingstill remains.

For example, in Patent Document 1 (JP-A-2003-5313) a stereoscopic imageshooting apparatus in which the convergence point can be adjusted to anarbitrary position with the focus point of the camera coinciding withthe convergence point of two eyes is described. Using the apparatus,shooting can be performed with the IAD equal to the pupil distance of ahuman and, in the case of close-in shooting, videos with naturalstereoscopic effects may be shot.

SUMMARY

However, in the configurations described in Patent Document 1,specifically in FIGS. 3A and 3B and 5A, and 5B, for bringing theconvergence point and the focus point to coincide with each other, it isconsidered to be necessary that the imaging optical system is focused oninfinity. In this case, in normal shooting, i.e., shooting in the stateof on-focus in which a moving subject is constantly focused on or thelike, it is considered that the shot videos are very unnatural. Forexample, when the subject moves forward and backward, videos in whichthe subject itself does not move forward or backward, but thesurrounding landscape moves forward and backward are shot. That is, inthe stereoscopic image shooting apparatus described in Patent Document1, there are problems that it is impossible to change the focus withoutchanging the on-screen position or change the on-screen position withoutchanging the focus.

Thus, it is desirable to perform shooting of stereoscopic images with ashort base line length with image quality and functions maintained.

A stereoscopic imaging apparatus according to an embodiment of thepresent disclosure includes an objective optical system having afunction of imaging a subject as a real image or a virtual image, andplural imaging optical systems that image plural subject luminous fluxesoutput from different paths of the objective optical system again asparallax images using plural independent optical systems. Further, inthe case where a focal length value when the objective optical systemimages the subject as the real image is positive and the focal lengthvalue when the objective optical system images the subject as thevirtual image is negative, a focal distance (f) of the objective opticalsystem and a distance (L) from a rear principal point of the objectiveoptical system to a front principal point of the imaging optical systemis set to values that satisfy the following equation:|f/(L−f)|≤1.

According to the configuration, substantial pupils (effective pupils)are formed between the subject and the objective optical system orbetween the objective optical system and the imaging optical systems,and images obtained through the effective pupils are imaged. Further, bysetting the focal distance of the objective optical system and thedistance (L) from the rear principal point of the objective opticalsystem to the front principal point of the imaging optical system to thevalues that satisfy the above described equation, the distance betweenthe effective pupils may be made shorter than an actual base line lengthdetermined depending on a distance between lenses of the plural imagingoptical systems. Therefore, shooting of stereoscopic images may beperformed with the shorter base line length while keeping image qualityand functions without reducing the diameters of the lenses and the sizesof imagers of the imaging apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration example of astereoscopic imaging apparatus according to one embodiment of thepresent disclosure.

FIG. 2 is an optical path diagram showing paths in which beams passingthrough principal points of lenses of imaging optical systems of beamsradiated from a subject travel according to one embodiment of thepresent disclosure.

FIGS. 3A and 3B are explanatory diagrams for explanation of a principleof formation of effective pupils according to one embodiment of thepresent disclosure, and FIG. 3A is an optical path diagram showing pathsin which a beam in parallel to the optical axis of the beams radiatedfrom a certain point of a subject and a beam passing through the lenscenter of an objective optical system travel and FIG. 3B is an opticalpath diagram showing paths in which beams radiated from the lens centerof the imaging optical system travel.

FIG. 4 is an optical path diagram showing paths in which a beam inparallel to the optical axis and a beam passing through the lens centerof the objective optical system of beams radiated from the lens centerof the imaging optical system travel according to one embodiment of thepresent disclosure.

FIGS. 5A and 5B are explanatory diagrams for explanation of acalculation method of an effective IAD according to one embodiment ofthe present disclosure, and FIG. 5A is an optical path diagram showingpaths of beams in parallel to the optical axis of beams passing throughthe effective pupils and FIG. 5B extracts and shows only a partnecessary for calculation of the effective IAD of the information shownin FIG. 5A.

FIGS. 6A and 6B are explanatory diagrams for explanation of acalculation method of effective pupil positions according to oneembodiment of the present disclosure, and FIG. 6A is an optical pathdiagram showing paths of beams in parallel to the optical axis of beamsradiated from the lens centers of the imaging optical systems and FIG.6B extracts and shows only a part necessary for calculation of theeffective pupil positions of the information shown in FIG. 6A.

FIGS. 7A to 7C are explanatory diagrams showing changes of the effectiveIAD when the width of an imaging optical system IAD is changed accordingto one embodiment of the present disclosure, FIG. 7A shows an examplewhen the imaging optical system IAD is taken narrower, FIG. 7B shows anexample when the imaging optical system IAD is taken longer than thatshown in FIG. 7A, and FIG. 7C shows an example when the imaging opticalsystem IAD is taken longer than that shown in FIG. 7B.

FIGS. 8A to 8C are explanatory diagrams showing changes of the effectiveIAD when the distance from the rear principal point of the objectiveoptical system to the front principal point of the imaging opticalsystem, FIG. 8A shows an example when the distance from the rearprincipal point of the objective optical system to the front principalpoint of the imaging optical system is taken wider, FIG. 8B shows anexample when the distance from the rear principal point of the objectiveoptical system to the front principal point of the imaging opticalsystem is taken narrower than that shown in FIG. 8A, and FIG. 8C showsan example when the distance from the rear principal point of theobjective optical system to the front principal point of the imagingoptical system is taken narrower than that shown in FIG. 8B.

FIGS. 9A to 9C are explanatory diagrams showing changes of the effectiveIAD when the focal length of the objective optical system is changedaccording to one embodiment of the present disclosure, FIG. 9A shows anexample when the focal length is taken narrower, FIG. 9B shows anexample when the focal length is taken wider than that shown in FIG. 9A,and FIG. 9C shows an example when the focal length is taken wider thanthat shown in FIG. 9B.

FIG. 10 is an optical path diagram showing paths in which beams radiatedfrom the subject and passing through the lens center of the imagingoptical system pass when the subject moves in the optical axis directionaccording to one embodiment of the present disclosure.

FIG. 11 is a block diagram showing a configuration example of astereoscopic imaging apparatus according to a modified example of oneembodiment of the present disclosure.

FIG. 12 is an optical path diagram showing paths in which beams passingthrough the principal points of lenses of imaging optical systems ofbeams radiated from a subject travel according to a modified example ofone embodiment of the present disclosure.

FIGS. 13A and 13B are explanatory diagrams for explanation of aprinciple of formation of effective pupils according to the modifiedexample of one embodiment of the present disclosure, and FIG. 13A is anoptical path diagram showing paths in which a beam in parallel to theoptical axis and a beam passing through the lens center of an objectiveoptical system of the beams radiated from a certain point of the subjecttravel and FIG. 13B is an optical path diagram showing paths in whichbeams radiated from the lens center of the imaging optical systemtravel.

FIG. 14 is an optical path diagram showing paths in which a beam inparallel to the optical axis and a beam passing through the lens centerof the objective optical system of beams radiated from the lens centerof the imaging optical system travel according to the modified exampleof one embodiment of the present disclosure.

FIGS. 15A and 15B are explanatory diagrams for explanation of acalculation method of an effective IAD according to the modified exampleof one embodiment of the present disclosure, and FIG. 15A is an opticalpath diagram showing paths of beams in parallel to the optical axis ofbeams passing through the effective pupils and FIG. 15B extracts andshows only a part necessary for calculation of the effective IAD of theinformation shown in FIG. 15A.

FIG. 16 depicts an end-on view arrangement of imaging optical systemsand an objective optical system.

DETAILED DESCRIPTION

As below, embodiments for implementing the present disclosure will beexplained. The explanation will be made in the following order.

1. Configuration Example of Stereoscopic Imaging apparatus

2. Various modified Examples

1. Configuration Example of Stereoscopic Imaging Apparatus

[Overall Configuration Example of Stereoscopic Imaging Apparatus]

FIG. 1 shows a configuration example of a stereoscopic imaging apparatusaccording to a first embodiment of the present disclosure. Thestereoscopic imaging apparatus 1 includes an objective optical system 10having a function of imaging a subject S as a real image and two imagingoptical systems 20 a, 20 b that respectively image plural subjectluminous fluxes output from different paths of the objective opticalsystem 10 as parallax images again. In the embodiment, a convex lens isused for the objective optical system 10. Note that, in the exampleshown in FIG. 1, for the explanation to be easily understood, theobjective optical system 10 is a thin lens having a focal length f, theimaging optical systems 20 a, 20 b include thin lenses 201 a, 201 b andimagers 202 a, 202 b, respectively. The actual objective optical system10 includes multiple or multiple groups of lenses, filters, diaphragms,lens drive mechanisms, etc. Further, in addition to the mechanisms, azoom function, a focusing function, and other functions may be provided.The imaging optical systems 20 a, 20 b also actually include multiple ormultiple groups of lenses, filters, diaphragms, lens drive mechanisms,etc., and may have a zoom function, a focusing function, and otherfunctions. In the configuration shown in FIG. 1, the objective opticalsystem 10 and the imaging optical systems 20 a, 20 b are placed so thatan optical axis A1 of the objective optical system 10 and optical axesA2 a, A2 b of the respective imaging optical system 20 a, 20 b may existon the same plane.

[Formation Example of Effective IAD in Stereoscopic Imaging Apparatus]

Next, a substantial IAD (hereinafter, referred to as “effective IAD”)formed in the stereoscopic imaging apparatus 1 will be explained withreference to FIG. 2. FIG. 2 is an optical path diagram showing paths inwhich beams passing through principal points of lenses of the imagingoptical systems 20 a, 20 b of beams radiated from a subject S travel.The luminous fluxes radiated from the subject S are allowed to enter theobjective optical system 10, then, guided by the two imaging opticalsystems 20 a, 20 b and imaged on the imagers 202 a and 202 b, andrespectively form parallax images. In this regard, the beams passingthrough a front principal point fH20 a of the lens of the imagingoptical system 20 a and the beams passing through a front principalpoint fH20 b of the lens of the imaging optical system 20 b areconsidered. For example, the group of beams passing through theprincipal point fH20 a of the imaging optical system 20 a are upperbeams shown by broken lines and the beams passing through the principalpoint fH20 b of the imaging optical system 20 b are lower beams shown bysolid lines. Further, the beams shown by the broken lines and the beamsshown by the solid lines respectively pass through two effective pupils(hereinafter, referred to as effective pupils EP) virtually existingbetween the subject S and the objective optical system 10. Then, thesubject S seen from the positions of the effective pupils EP is imagedon the imager 202 a of the imaging optical system 20 a and the imager202 b of the imaging optical system 20 b. That is, the distance betweenthese two effective pupils EP (hereinafter, referred to as “effectiveIADed”) is the substantial IAD in the stereoscopic imaging apparatus 1.The principle of formation of the effective pupils EP between thesubject S and the objective optical system 10 will be described laterwith reference to FIGS. 3A, 3B, and 4.

The effective IADed is expressed by the following equation 1.ed=f/(L−f)×d  (Eq. 1)

In the equation 1, “f” is a focal length of the objective optical system10, “L” is a distance from a rear principal point rH10 of the objectiveoptical system 10 to the front principal point fH20 a of the imagingoptical system 20 a and the front principal point fH20 b of the imagingoptical system 20 b. Note that, when the optical system is idealized asthe thin lens as shown in FIG. 2, there is no distinction made betweenthe front principal point and the rear principal point, and the frontprincipal point and the rear principal point coincide with the principalpoint. Further, “d” is an IAD determined depending on the placementpositions of the imaging optical system 20 a and the imaging opticalsystem 20 b, and generally, refers to the distance between frontprincipal points of the imaging optical systems, i.e., the distancebetween the front principal points fH20 a and fH20 b of the imagingoptical system 20 a and the imaging optical system 20 b.

For example, the focal length f of the objective optical system 10 is 70mm and the distance L is 370 mm. Further, the imaging optical system 20a and the imaging optical system 20 b are separately placed at adistance d=60 mm with the optical axis A1 of the objective opticalsystem 10 as an axis of symmetry (imaging optical system IADd=60 mm). Inthis case, the effective IADed is calculated to be 14 mm by the aboveequation 1. This means that, compared to the imaging optical system IADd(60 mm) obtained depending on the placement positions of the imagingoptical systems 20 a and 20 b, the substantial IAD (effective IADed) maybe made shorter to f/(L−f) times (14 mm).

Therefore, by setting the focal length f and the distance L of theobjective optical system 10 to values that satisfy the followingequation 2, the effective IADed may be made shorter than the imagingoptical system IADd obtained depending on the placement positions of theimaging optical systems 20 a and 20 b. Note that the following equationis on the assumption that a convex lens is used as the lens of theobjective optical system 10 and its focal length f is positive (f>0).f/(L−f)≤1  (Eq. 2)[Principle of Formation of Effective Pupils in Stereoscopic ImagingApparatus]

Next, in the stereoscopic imaging apparatus 1, the principle of virtualformation of effective pupils between the subject S and the objectiveoptical system 10 will be explained with reference to FIGS. 3A, 3B, and4. First, a spatial image S′ formed by the objective optical system 10will be explained with reference to FIG. 3A, and then, beam paths fromthe subject S to the imager 202 a (202 b) will be explained withreference to FIG. 3B. Then, a mechanism of formation of the effectivepupils will be explained with reference to FIG. 4.

(1) Regarding Spatial Image

As shown in FIG. 3A, the luminous fluxes radiated from the subject Spass through the objective optical system 10 and is imaged again, andthereby, the spatial image S′ is formed between the objective opticalsystem 10 and the imaging optical systems 20 a, 20 b. The spatial imageS′ is seen as if there was an object in its position, and may be seenfrom the view points of the lenses of the imaging optical systems 20 a,20 b. The principle of formation of the spatial image S′ is easilyunderstood by considering two beams of a beam in parallel to the opticalaxis A1 of the beams radiated from a certain point of the subject S anda beam passing through the center of the lens of the objective opticalsystem 10. The beam in parallel to the optical axis A1 of the beamsoutput from a certain point of the subject S becomes a beam passingthrough the focal point F of the objective optical system 10 afterpassing through the lens because of the property of the lens of theobjective optical system 10. On the other hand, the beam passing throughthe center of the lens of the objective optical system 10 travels in astraight line without change because of the property of the lens. Then,these two beams intersect at another point again. The intersection pointis a point in the spatial image S′ corresponding to the subject S thathas radiated the beams.

(2) Beam Paths from Subject to Imager of Imaging Optical System

As shown in FIG. 3B, if beams are radiated from the centers of thelenses of the imaging optical systems 20 a, 20 b, the beams radiatedfrom the subject S travel in the same paths as those of those beams.Accordingly, the paths are easily understood by consideration from thecenters of the lenses of the imaging optical systems 20 a, 20 b. In theexample shown in FIG. 3B, the path in which the beam radiated from thecenter of the lens of the imaging optical system 20 a travels will beexplained as an example. The beam radiated from the center of the lensof the imaging optical system 20 a passes through a certain point of thespatial image S′, then, reaches the lens of the objective optical system10, and travels toward a certain point of the subject S corresponding to“certain point of spatial image S′”. The beam from the center of thelens of the imaging optical system 20 a to the imager 202 a may beobtained by extending the beam passing through the lens center of theimaging optical system 20 a to the position of the imager 202 a withoutchange.

(3) Regarding Effective Pupils

Subsequently, the principle of formation of the effective pupils EP willbe explained with reference to FIG. 3B. The creation of the beam pathfrom the subject S to the imager 202 a of the imaging optical system 20a as described above is performed with respect to the beams passingthrough other points of the spatial image S′. Then, it is known that thebeams radiated from the lens center of the imaging optical system 20 aintersect at a certain point again after passing through the objectiveoptical system 10. This point is the effective pupil EP. The effectivepupil EP is a point that all beams to pass through the lens center ofthe imaging optical system 20 a pass. Accordingly, the picture imaged onthe imaging surface of the imager 202 a of the imaging optical system 20a is a picture equal to an image shot using the effective pupil EP as apupil. That is, by imaging the subject S using the stereoscopic imagingapparatus 1 according to the embodiment, the same picture as the pictureshot by a camera placed in the position of the effective pupil EP can beacquired.

The position where the effective pupil EP is formed may be obtained alsoby considering the beam in parallel to the optical axis A1 of the beamsradiated from the lens center of the imaging optical system 20 a and thebeam passing through the lens center of the objective optical system 10.As described above, if beams are radiated from the center of the lens ofthe imaging optical system 20 a, the beams radiated from the subject Stravel in the same paths as the paths in which those beams travel. Thismeans that, if a light emitting point is placed at the lens center ofthe imaging optical system 20 a, all of the beams radiated from thepoint pass through the effective pupil EP. That is, the effective pupilEP is “shadow of lens” or “spatial image” of the imaging optical system20 a. Therefore, as shown in FIG. 4, it is known that the effectivepupil EP is formed at the point at which the beam in parallel to theoptical axis A1 of the beams radiated from the lens center of theimaging optical system 20 a and the beam passing through the lens centerof the objective optical system 10 intersect again.

[Calculation Method of Effective IAD]

As described above, the effective pupil EP is the point at which allbeams from the subject S toward the lens center of the imaging opticalsystem 20 a (20 b) pass. These beams include beams in parallel to theoptical axis A1. To obtain the effective IADed, consideration of thebeams in parallel to the optical axis A1 is easily understood. In FIG.5A, the paths of the beams in parallel to the optical axis A1 of thebeams passing through the effective pupils EP are shown by broken lines.The beams in parallel to the optical axis A1 passing through theeffective pupils EP pass through the lens of the objective opticalsystem 10, and then, travel toward the focal point F of the lens of theobjective optical system 10 because of the property of the lens. Thebeams that have passed through the focal point F travel toward thecenters of the respective lenses of the imaging optical systems 20 a, 20b according to the definition of the effective pupils EP.

FIG. 5B extracts only a characteristic part necessary for obtainment ofthe effective IADed of the information shown in FIG. 5A. In the drawing,two triangles having similarity shapes to each other are shown. One is ashaded larger triangle having a bottom side of the imaging opticalsystem IADd as the distance between the respective lenses of the imagingoptical systems 20 a, 20 b and a height of (distance L—objective opticalsystem focal length f). The other one is a hatched smaller trianglehaving a bottom side of the effective IADed as the distance between thetwo effective pupils EP and a height of the focal length f of theobjective optical system 10. These two triangles have similarity shapesto each other, and they are expressed by the following equations becauseof their property.Effective IADed: Imaging optical system IADd=Objective optical systemfocal length f: Distance L−Objective optical system focal length f

Therefore,ed×(L−f)=f×d, anded=f/(L−f)×d  Eq. (1)is calculated.

The position of the effective pupil EP in the optical axis direction maybe calculated using the focal length f of the lens of the objectiveoptical system 10, the imaging optical system IADd, and the effectiveIADed. FIG. 6A shows paths of beams in parallel to the optical axis A ofbeams radiated from the respective lens centers of the imaging opticalsystems 20 a, 20 b. The beam radiated from the center of the lens of theimaging optical system 20 a and the beam radiated from the center of thelens of the imaging optical system 20 b reach the lens of the objectiveoptical system 10 and pass through the lens, and becomes beams passingthrough the focal point F of the objective optical system 10. Then,after passing through the focal point F, the beams respectively passthrough the two effective pupils EP and travel toward the subject S (notshown).

FIG. 6B extracts only a characteristic part necessary for obtainment ofthe positions of the effective pupils in the optical axis direction ofthe information shown in FIG. 6A. In the drawing, two triangles havingsimilarity shapes to each other are shown. One is a shaded largertriangle having a bottom side of the imaging optical system IADd and aheight of the effective pupil objective optical system focal length f.The other one is a hatched smaller triangle having a bottom side of theeffective IADed and a height of the distance from the focal point F tothe effective pupil EP (hereinafter, referred to as “effective pupilposition EPd”). These two triangles have similarity shapes to eachother, and they are expressed by the following equations because oftheir property.Effective IADed: Imaging optical system IADd=Effective pupil positionEPd: Objective optical system focal length f

Therefore,ed×f=d×EPd, andEPd=(ed×f)/d  Eq. (3)is calculated.

Next, formation examples of the effective IADed according to thestereoscopic imaging apparatus 1 of the embodiment will be explainedwith reference to FIGS. 7A to 9C. The effective IADed may be calculatedusing the above described equation 1. That is, by changing the objectiveoptical system focal length f, the distance L, and the imaging opticalsystem IADd, the effective IADed may be changed. That is, by changingthese parameters, the effective IADed having an arbitrary length may berealized.

FIGS. 7A to 7C show examples when the width (length) of the effectiveIADed is changed by changing the imaging optical system IADd (thedistance between the respective lenses of the imaging optical systems 20a, 20 b). The same signs are assigned to the parts corresponding tothose in FIG. 2, and their detailed explanation will be omitted. FIG. 7Ashows an example when the imaging optical system IADd is set narrower(to the width shown in FIGS. 1 to 6B) and FIG. 7B shows an example whenthe imaging optical system IADd is made wider than that shown in FIG.7A. FIG. 7C shows an example when the imaging optical system IADd ismade wider than that shown in FIG. 7B. As shown in FIGS. 7A to 7C, it isknown that the wider the imaging optical system IADd, the wider theeffective IADed.

FIGS. 8A to 8C show examples when the width of the effective IADed ischanged by changing the distance L (the distance from the rear principalpoint rH10 of the objective optical system 10 to the front principalpoint fH20 a (fH20 b) of the imaging optical system 20 a (20 b)). Thesame signs are assigned to the parts corresponding to those in FIG. 2,and their detailed explanation will be omitted. FIG. 8A shows an examplewhen the distance L is taken wider and FIG. 8B shows an example when thedistance L is made shorter than that shown in FIG. 8A. Further, FIG. 8Cshows an example when the distance L is made shorter than that shown inFIG. 8B. As shown in FIGS. 8A to 8C, it is known that the shorter thedistance L, the wider the effective IADed.

Note that, as shown in FIG. 8C, by setting the distance L (and the focallength·f) to satisfy f/(L−f)>1, the effective IADed can be made widerthan the imaging optical system IADd. For example, the focal length f ofthe objective optical system 10 is 70 mm, the distance L is 105 mm, andthe Imaging optical system IADd is 60 mm. In the case of theconfiguration, the imaging optical system IADd is calculated to be 120mm by the above described equation 1. That is, compared to the imagingoptical system IADd (60 mm) obtained depending on the placementpositions of the imaging optical systems 20 a and 20 b, the effectiveIADed may be made longer to f/(L−f) times.

FIGS. 9A to 9C show examples when the effective IADed is changed bychanging the focal length f of the objective optical system 10. Thefocal length f may be changed by using lenses with different focallengths f and using zoom lenses. In FIGS. 9A to 9C, the same signs areassigned to the parts corresponding to those in FIG. 2, and theirdetailed explanation will be omitted. FIG. 9A shows an example when thefocal length f is made narrower, and FIG. 9B shows an example when thefocal length f is made longer than that shown in FIG. 9A. Further, FIG.9C shows an example when the focal length f is made longer than thatshown in FIG. 9B. As shown in FIGS. 9A to 9C, it is known that thelonger the focal length f of the lens of the objective optical system10, the wider the effective IADed.

As described above, according to the stereoscopic imaging apparatus 1 ofthe embodiment, by selecting the focal length f of the objective opticalsystem 10, the parameter (distance L) related to the positions of theimaging optical systems 20 a, 20 b, and the imaging optical system IADd,the substantial IAD of the stereoscopic imaging apparatus 1 may beselected. Therefore, the degree of freedom of design of the stereoscopicimaging apparatus 1 may be improved.

Further, by setting the focal length f of the lens of the objectiveoptical system 10 and the distance L to values that satisfy the equation2, the substantial IAD (effective IADed) may be made shorter than theactual IAD (imaging optical system IADd) determined depending on theplacement positions of the imaging optical systems 20 a and 20 b.Therefore, the range of parallax within one screen may be limited withina fixed range. Thereby, contents that impose large burdens on viewerssuch as contents having large amounts of pop out and depths from thescreen and contents with parallax that largely changes at times when thescene changes are not shot. Thus, discomfort of eye strain and typicalfatigue that viewers viewing the contents feel may be reduced.Furthermore, the important IAD from 10 mm to 40 mm most frequently usedwhen near distance shooting is performed may be easily realized.

In addition, the effective IADed of the stereoscopic imaging apparatus 1may be made shorter without bringing the placement positions of theimaging optical systems 20 a and 20 b closer, and thus, it is notnecessary to reduce the sizes of the imagers or attach lenses havingsmaller diameters. That is, the effective IADed of the stereoscopicimaging apparatus 1 may be made shorter without deterioration of theperformance of the camera main body such as resolution and sensitivity.Therefore, even in the stereoscopic imaging apparatuses of theside-by-side method and the integrated method that are difficult toreduce the distance between lenses, shooting with the shorter IAD may beeasily performed.

Further, by setting the focal length f of the lens of the objectiveoptical system 10 and the distance L to satisfy f/(L−f)>1, the effectiveIADed can be made wider than the imaging optical system IADd. Accordingto the configuration, even in an apparatus that may only have aphysically narrow IAD such as an endoscope, for example, videos withmore stereoscopic effects may be shot.

Furthermore, the effective pupil EP formed in the stereoscopic imagingapparatus 1 are the points at which all beams from the subject S towardthe lens centers of the imaging optical systems 20 a, 20 b pass.Accordingly, for example, even when the subject S moves from position Ato position B as shown in FIG. 10, all of the beams radiated from theposition of the subject S in the position B and passing through lenscenters of the imaging optical systems 20 a, 20 b pass through theeffective pupils EP. Thereby, even when the subject S is movable, thesame moving images as those when the camera is placed in the effectivepupil position EPd may be shot. Therefore, functions of moving focus(focus position) of the imaging optical systems 20 a, 20 b to a desiredposition within a finite distance and control it can be additionallyprovided. Accordingly, for example, the focal lengths of the two imagingoptical systems 20 a, 20 b may be controlled in a ganged manner andshooting may be performed constantly in focus on the moving subject S.By performing the shooting, normal and natural videos in which thesubject S on the display screen moves forward and backward to themovement of the subject S may be shot.

In addition, according to the stereoscopic imaging apparatus 1 of theembodiment, unlike the technology shown as Patent Document 1, it is notnecessary to constantly bring the convergence point and the focus tocoincide with each other. Therefore, the convergence point may beadjusted by the imaging optical system 20 a (20 b) or the objectiveoptical system 10, the focus may be adjusted by the imaging opticalsystem 20 a (20 b) or the objective optical system 10, and the angle ofview may be adjusted by the imaging optical system 20 a (20 b) or theobjective optical system 10. That is, the parameters for shooting may beset by individually adjusting the objective optical system 10 and theimaging optical system 20 a (20 b).

2. Various Modified Examples

In the above described embodiment, the example in which the two imagingoptical systems are provided has been cited, however, more of them maybe provided. For example, as shown in FIG. 11, three of them may beprovided such as imaging optical systems 20 a, 20 b, 20 c. Further, theobjective optical system 10 and the imaging optical systems 20 a, 20 b,20 c may be placed so that the optical axis A1 of the objective opticalsystem 10 and the respective optical axes A2 a, A2 b, A2 c of theimaging optical systems 20 a, 20 b, 20 c may exist on different planes,as depicted in FIG. 16. According to the configuration, parallaxinformation in the vertical direction may be obtained, and, for example,shooting when assuming that a viewer of stereoscopic images views theimages in a posture of lying down or the like may be performed.

Further, in the above described embodiment, the example in which theconvex lens is used for the lens of the objective optical system 10 hasbeen cited for explanation, however, a concave lens may be used.Configuration examples using a concave lens will be explained withreference to FIGS. 12 to 15B. FIG. 12 shows a configuration example of astereoscopic imaging apparatus when a concave lens is used for anobjective optical system. In FIG. 12, the same signs are assigned toparts corresponding to those in FIG. 2, and their detailed explanationwill be omitted. In the example shown in FIG. 12, a concave lens is usedas a lens of an objective optical system 10α, and the focal length f isformed nearer the subject side S. Accordingly, the effective pupils EPare formed between the objective optical system 10α and the imagingoptical system 20 a and the imaging optical system 20 b.

FIGS. 13A and 13B are diagrams for explanation of a principle offormation of the effective pupils EP between the objective opticalsystem 10α and the imaging optical systems 20 a, 20 b in an stereoscopicimaging apparatus 1α using the concave lens. In FIGS. 13A and 13B, thesame signs are assigned to parts corresponding to those in FIGS. 3A and3B, and their detailed explanation will be omitted. In the case wherethe concave lens is used for the objective optical system, a virtualimage V is formed between the subject S and the objective optical system10α. As is the case explained with reference to FIGS. 3A and 3B, theposition in which the virtual image V is formed is easily understood byconsidering two beams of a beam in parallel to the optical axis A1 ofthe beams radiated from a certain point of the subject S and a beampassing through the center of the lens of the objective optical system10α. As shown in FIG. 13A, the virtual image V is formed in a positionin which an auxiliary line aL drawn from the point at which the beam inparallel to the optical axis A1 collides with the lens of the objectiveoptical system 10α toward the focal point F of the objective opticalsystem 10α and the beam passing through the center of the lens of theobjective optical system 10α intersect.

FIG. 13B shows paths in which beams radiated from the center of the lensof the imaging optical system 20 b travel. The actual beams radiatedfrom the lens center of the imaging optical system 20 b travel towardthe subject S in the paths shown by solid lines. On the other hand,apparent beams when seen from the view point on the lens of the imagingoptical system 20 b pass through the objective optical system 10α, andthen, travel toward the virtual image V in the path shown by auxiliarylines aL shown by broken lines. Further, the apparent beams certainlypass through the effective pupil EP in the position located in extensionof the auxiliary line aL in an opposite direction to the objectiveoptical system 10α. That is, the video formed on the imager 202 b of theimaging optical system 20 b is equal to a video shot using the effectivepupil EP as a pupil.

Furthermore, even in the case of using the concave lens, the positionsin which the effective pupils EP are formed may be obtained byconsideration of the beam in parallel to the optical axis A1 of thebeams radiated from the lens center of the imaging optical system 20 band the beam passing through the lens center of the lens of theobjective optical system 10α. FIG. 14 shows paths in which beamsradiated from the center of the lens of the imaging optical system 20 btravel. In FIG. 14, the same signs are assigned to the partscorresponding to those in FIG. 4, and their detailed explanation will beomitted. In FIG. 14, an auxiliary line aL between the focal point F ofthe objective optical system 10α and the point at which the beam inparallel to the optical axis A1 collides with the lens of the objectiveoptical system 10α is shown by a broken line. Further, an effectivepupil EP is formed in a position in which the beam radiated from thecenter of the lens of the imaging optical system 20 b and shown by asolid line and the auxiliary line aL intersect. This means that, if alight emitting point is placed at the lens center of the imaging opticalsystem 20 b, all beams radiated from the point pass through theeffective pupil EP. That is, the effective pupil EP is “shadow of lens”or “virtual image” of the imaging optical system 20 b.

FIGS. 15A and 15B are diagrams for explanation of a calculation methodof an effective IADed when the concave lens is used for the objectiveoptical system 10α. In FIGS. 15A and 15B, the same signs are assigned tothe parts corresponding to those in FIGS. 5A and 5B, and their detailedexplanation will be omitted. FIG. 15A shows paths of beams in parallelto the optical axis A1 of beams from the subject S (not shown) towardthe lens centers of the imaging optical systems 20 a (20 b). The pathsin which the beams actually travel are shown by solid lines and apparentbeams seen from view points of the lenses of the imaging optical systems20 a and 20 b are shown by broken lines. Further, the beams in parallelto the optical axis A1 shown by the solid lines and the apparent beamsshown by the broken lines collide with the objective optical system 10α,and then, intersect at two points. The distance between the two pointsis an effective IADed.

FIG. 15B extracts only a characteristic part necessary for obtainment ofthe effective IADed of the information shown in FIG. 15A. In thedrawing, two triangles having similarity shapes to each other are shown.One is a shaded larger triangle having a bottom side of the imagingoptical system IADd as the distance between the respective lenses of theimaging optical systems 20 a, 20 b and a height of (objective opticalsystem focal length f+distance L). The other one is a hatched smallertriangle having a bottom side of the effective IADed and a height of thefocal length f of the objective optical system 10α. These two triangleshave similarity shapes to each other, and they are expressed by thefollowing equation 4 because of their property.Effective IADed: Imaging optical system IADd=Objective optical systemfocal length f: Distance L+Objective optical system focal length f

Further, since the focal length f when the concave lens is used isnegative (f<0),ed×(L+(−f))=f×d, anded=|f/(L−f)|×d  Eq. (4)is calculated.

That is, in both the case of using the convex lens and the case of usingthe concave lens for the lens of the objective optical system 10, theeffective IADed may be calculated using the equation 4. Further, in boththe case of using the convex lens and the case of using the concave lensfor the lens of the objective optical system 10, by setting the focallength f of the objective optical system 10 and the distance L tosatisfy the following equation 5, the effective IADed may be madeshorter than the actual imaging optical system IADd.|f/(L−f)|≤1  (Eq. 5)

In this manner, even when the concave lens is used for the lens of theobjective optical system 10, the same advantage as that when the convexlens is used may be obtained. Further, when the concave lens is used,because the focal length f is negative compared to the case where theconvex lens is used, the distance L necessary for realization of thesame effective IADed for the same focal length |f| and the same imagingoptical system IADd as those when the convex lens is used can be takenshorter. Therefore, the stereoscopic imaging apparatus 1α may be formedto be smaller.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2010-251750 filed in theJapan Patent Office on Nov. 10, 2010, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An endoscope comprising: an objective opticalsystem configured to image a subject as a real image or a virtual image;two separated imaging optical systems configured to form images fromplural subject luminous fluxes output from different paths of theobjective optical system again as parallax images; and two virtualeffective pupils located a first distance and a second distance from theobjective optical system and spaced apart from an optical axis of theobjective optical system, wherein a distance between central points ofthe two virtual effective pupils is less than a distance separatingoptical axes of the imaging optical systems, wherein the luminous fluxesconverge through the two virtual effective pupils.
 2. The endoscopeaccording to claim 1, wherein a focus point of each of the imagingoptical systems is set to a predetermined position within a finitedistance.
 3. The endoscope according to claim 1, wherein the objectiveoptical system and the imaging optical systems are placed so that theiroptical axes are located on a same plane.
 4. The endoscope according toclaim 1, wherein the objective optical system and the imaging opticalsystems are placed so that their optical axes are located on differentplanes.
 5. The endoscope according to claim 1, wherein in the case wherea focal length value when the objective optical system images thesubject as the real image is positive and the focal length value whenthe objective optical system images the subject as the virtual image isnegative, a focal distance (f) of the objective optical system and adistance (L) from a rear principal point of the objective optical systemto a front principal point of the imaging optical systems is set tovalues that satisfy the following equation|f/(L−f)|<1.
 6. The endoscope according to claim 1, wherein the twoimaging optical systems include plural imagers.
 7. The endoscopeaccording to claim 1, wherein no lensing system is located between theobjective optical system and the two imaging optical systems.
 8. Theendoscope according to claim 1, wherein the objective optical systemcomprises multiple lenses.
 9. An imaging apparatus comprising: anobjective optical system configured to image a subject as a real imageor a virtual image; and two separated imaging optical systems configuredto form images from plural subject luminous fluxes output from differentpaths of the objective optical system again as parallax images; and twovirtual effective pupils located a first distance and a second distancefrom the objective optical system and spaced apart from an optical axisof the objective optical system, wherein a distance between centralpoints of the two virtual effective pupils can be made less than adistance separating optical axes of the imaging optical systems, whereinthe luminous fluxes converge through the two virtual effective pupils.10. The imaging apparatus according to claim 9, wherein a focus point ofeach of the imaging optical system is set to a predetermined positionwithin a finite distance.
 11. The imaging apparatus according to claim9, wherein the objective optical system and the imaging optical systemsare placed so that their optical axes are located on a same plane. 12.The imaging apparatus according to claim 9, wherein the objectiveoptical system and the imaging optical systems are placed so that theiroptical axes are located on different planes.
 13. The imaging apparatusaccording to claim 9, wherein in the case where a focal length valuewhen the objective optical system images the subject as the real imageis positive and the focal length value when the objective optical systemimages the subject as the virtual image is negative, a focal distance(f) of the objective optical system and a distance (L) from a rearprincipal point of the objective optical system to a front principalpoint of the imaging optical system is set to values that satisfy thefollowing equation|f/(L−f)|≤1.
 14. The imaging apparatus according to claim 9, wherein thetwo imaging optical systems include plural imagers.
 15. The imagingapparatus according to claim 9, wherein no lensing system is locatedbetween the objective optical system and the two imaging optical system.16. The imaging apparatus according to claim 9, wherein a separation ofthe virtual effective pupils is different from a separation betweenoptical axes of the imaging optical systems.
 17. The imaging apparatusaccording to claim 9, wherein the objective optical system comprisesmultiple lenses.